Influence of masterbatch on crosslinking of liquid silicone rubbers

Siloxanes represent polymers that can occur in several forms, enabling the production of materials with diverse structures. The proportion of organic and inorganic precursor units influences a wide range of siloxane polymer modifications. The immiscibility of different phases leads to microphase separation, which can be mitigated by improving component miscibility through chemical bonding or enhanced physical interactions. In this study, a reactive siloxane polymer containing vinyl groups and silicon(IV) oxide as a reinforcing filler was used to prepare a masterbatch for the crosslinking of liquid silicone rubbers (LSR). The masterbatch was incorporated at concentrations of up to 10 wt% in formulations with varying hydrogen siloxane to vinyl siloxane (H:Vi) ratios (40:60, 50:50, and 65:35). The crosslinking reaction was confirmed by FTIR spectroscopy, while TEM analysis revealed good dispersion of the filler within the polymer matrix. The results showed that the 50:50 H:Vi ratio with 5% masterbatch exhibited the most balanced mechanical properties, achieving a tensile strength of 10.00 MPa and a Shore A hardness of 54. However, FTIR analysis demonstrated that masterbatch addition had a dose-dependent inhibitory effect on crosslinking efficiency, which decreased from 97.0% (in the unfilled 50:50 sample) to 91.4% with 10% masterbatch. TGA analysis revealed that the 65:35 ratio with 10% masterbatch exhibited the highest thermal stability (Tons = 455 °C). The findings suggest that masterbatch composition can be tailored to achieve specific material properties, but its impact on crosslinking kinetics must be considered during formulation design.